Dental caries (commonly known as “cavities”) is a chronic infectious disease that is extremely difficult to completely eradicate. Tooth decay is caused by the demineralization of the tooth structure primarily originating in the enamel (hard tissue). Dental enamel is a thin layer, typically 1 to 2 mm thick, composed of a crystal-like structure of carbonated hydroxyapatite comprising 96% of enamel by weight and approximately 85% by volume. The balance of enamel, 15% by volume, is made up of water, protein, and lipid. Tooth decay is the result of dental acids, created by bacteria metabolizing sugars, which in turn de-mineralize the hydroxyapatite. The bacteria create a biofilm after 24 hours, referred to as plaque, which is soft and pliable, but after about 10 days the plaque hardens significantly to form dental calculus or tartar.
The majority of tooth decay occurs in the occlusal surface (top surface) and in unexposed areas between teeth. The lingual (back surface) and buccal (front surface) are relatively smooth compared to the occlusal surface, and therefore, trap less sugars to be metabolized resulting in relatively less dental acid and less decay than that in the occlusal surface and the unexposed areas between teeth. Decay is most likely in areas that cannot be brushed and cleaned easily such as pits and fissures on the occlusal surface, areas under the gums, and contact surfaces between the teeth.
Nevertheless, there has been a remarkable decline in dental caries over the last 60 years due to various new detection techniques such as digital x-rays, 3-D x-rays and fluorescence, prevention techniques including fluoride treatments and sealants, and new or improved treatment techniques including higher speed dental drills, smaller stronger burs, various wavelength laser technology, and ultrasonic cleaning equipment.
Detection: Analog x-rays have progressed to digital x-rays, and to cone beam 3-D x-rays, which have a higher resolution than the analog x-rays and are stored digitally while progressively using less and less radiation. Recently optical fluorescence has also been used to identify the bacterium that leads to tooth decay. Removing the fluorescing bacteria removes the carious tissue.
Prevention: Various fluoride treatments, new toothpastes, and mouthwashes have been introduced that re-mineralize the enamel, specifically with fluorapatite which has a higher resistance to dental acids than hydroxyapatite. Additionally flowable composites (commonly called epoxies) are referred to as “sealants,” and are added to the occlusal surface to prevent bacteria from getting down into pits and fissures.
Treatment: Dental drills have progressed from motor driven rope mechanisms to compressed air driven devices, and to electrical motor driven devices. The Food and Drug Administration (FDA) has approved five different laser types at seven different wavelengths for a variety of dental indications. There are single wavelength dental laser devices, multiple wavelength devices, and q-switched, continuous and pulsed laser products. There are various dental laser hand pieces and delivery mechanisms, but all of these laser products are manufactured to maximally or minimally couple into water. Peak water absorption is sought to cut enamel because, as previously stated, water is only a 4% or less constituent by weight, so peak water absorption is required to vaporize water thereby fracturing the enamel, albeit slowly. Minimal water absorption is sought to cut soft tissue, gums and cheeks, so that the blood is cauterized and bleeding is minimized.
Recently a new laser based dental treatment system was developed that employs a mid-infrared wavelength laser that couples primarily into hydroxyapatite and partially into water. The advantage of coupling into hydroxyapatite, which constitutes about 96% of hard tissue by weight, is faster cutting with greater resolution, while partially coupling into water allows for faster soft tissue cutting while cauterizing avoiding bleeding.
In parallel to the above-described dental technology advances, optical scanners, or spinning mirrors, have been used in material processing applications for more than three decades. The advantage of using scanning mirrors to reposition optical energy is that high accuracy positioning can be achieved while overcoming a minimal amount of inertia. Low inertia allows the positioning system to accelerate and decelerate rapidly while maintaining high positional accuracy. Over the last three decades, various spinning mirror geometries have evolved creating smaller, faster movements without compromising accuracy.
Despite these advances, laser-based dental treatment systems face several challenges. One of the most common problems relates to the shape of the area to be treated. A cavity in a tooth rarely has a regular shape such as a square, circle, or an oval. In order to fully treat the affected area using previously known methods, the operator typically treats a regular-shaped area that encompasses the affected area. This, however, can cause damage to tissue that is within the encompassing area but that is not affected.
There is yet another problem in treating even a regular-shaped area. The operator must be able to hold the hand piece used to direct a laser beam to the treatment area extremely steady and then be able to move it carefully within a selected area. Laser beams used for treatment are generally very powerful, and slight movement of the operator's hand or by the patient can cause the laser beam to be directed to tissue that does not require any treatment and can cause damage thereto. Furthermore, within the selected area, the laser energy must be applied uniformly, i.e., the operator must direct substantially the same amount of energy to each point within the selected treatment area. As the overall treatment area is typically on the order of a few square centimeters or even smaller, manually directing a laser beam to the desired treatment area is difficult and error prone. Therefore, there is a need for improved systems and methods of laser based dental treatment.